Botany

The conventional theory of how plants capture and channel energy from sunlight for photosynthesis was overturned in February 2010 by a radical theory based on quantum mechanics. Proteins called antennae absorb light energy, which excites electrons. According to classical ideas, the resulting energy is passed by energy hops down a molecular energy ladder. It eventually reaches proteins known as reaction centres, where chemical energy is generated. This operation is so fast that it is almost 100% efficient; however, the details have long remained a mystery. A team of scientists at the University of Toronto stimulated the photosynthetic antennae from algae with laser pulses lasting only femtoseconds (millionths of a billionth of a second) to mimic the absorption of sunlight. In experiments with dozens of antennae attached to one reaction centre, they discovered that the energy flowed through many different paths simultaneously to find the most efficient route—a phenomenon known as quantum coherence. The quantum coherence, in which energy exists in multiple linked states at the same time, lasted around 400 femtoseconds, or about 20 times longer than expected. “We were astonished to find clear evidence of long-lived quantum mechanical states involved in moving the energy,” said Greg Scholes, leader of the research group. Similar quantum coherence was also discovered in July in photosynthetic bacteria by a team at the University of California, Berkeley, and the Lawrence Berkeley National Laboratory. These findings raised the possibilities for creating artificial versions of photosynthesis by using quantum coherence for making highly efficient solar cells and vastly improving computer processor speeds.

In February parallels between plant and animal chemistry were highlighted by the report of the discovery of the sex hormone progesterone in a plant. Progesterone is a steroid hormone involved in animal reproduction. It was previously thought to be exclusive to animals; however, nuclear magnetic resonance and mass spectroscopy were used by scientists to spot progesterone in the leaves of the walnut tree (Juglans regia) and Adonis aleppica of the buttercup family (Ranunculaceae). “The significance of the unequivocal identification of progesterone from a higher plant cannot be overstated,” said Guido F. Pauli at the University of Illinois at Chicago. “New discoveries [such as this] indicate that plants and animals are more closely related than previously thought.” The discovery supported the idea that progesterone and other steroid hormones were inherited from an ancient common ancestor of plants and animal.

The genome of the apple (Malus domestica) was decoded by researchers from Italy, France, New Zealand, Belgium, and the United States. In a report published in August, they announced the complete genome sequence of around 13 billion nucleotides, the building blocks of DNA, in the Golden Delicious variety of apple. Among the approximately 57,000 genes identified, the complete set of 992 genes responsible for disease resistance was revealed. This research gave plant breeders an important resource for enhancing the apple’s texture, flavour, juice, and health properties. The work also enabled researchers to trace the origin of all roughly 7,500 apple varieties back to about 4,000 years ago to its common wild ancestor M. sieversii, which grew in the mountains of southern Kazakhstan.

The researchers also discovered that the relatively huge size of the apple genome appeared after the duplication of nearly all of its chromosomes. This explains why the genomes of the apple and the closely related pear (Pyrus) have 17 chromosomes, whereas all other fruit plants in the same Rosaceae family have between 7 and 9 chromosomes. “By duplicating almost all of its genome, apples now have very different fruit characteristics to related plants such as peaches, raspberries, and strawberries,” explained Sue Gardiner, a member of the research team based at New Zealand’s Plant and Food Research. “This suggests that a major environmental event forced certain species, including apple, to evolve for survival.” Evolutionary analysis dates the timing of the duplication to about 50 million years ago.

Research into wheat genetics made considerable progress in 2010. Data from the first attempt to sequence the wheat genome, performed by a team of British scientists at the Universities of Liverpool and Bristol and the John Innes Centre in Norwich, were released in August. The team sequenced 16 billion nucleotides in the largest genome decoded to date. The wheat genome was particularly complex because it was grouped into three sets of chromosomes, and each set originated from different ancestors of the original wheat plant. Thanks to recent advances in DNA technology, the genome was sequenced in only one year, compared with 13 years for the significantly smaller human genome. The researchers planned to compare the genomes of different wheat varieties to find the segments of DNA that control particular traits, such as fungal-disease resistance and tolerance to heat and drought. The earliest benefits were likely to emerge from conventional breeding using DNA markers, which will allow breeders to link desirable traits to segments of DNA and help them to pick plants for crossing. Wheat accounts for about 30% of global grain production, second to rice as the main human food crop. “It is predicted that within the next 40 years world food production will need to be increased by 50%. Developing new, low input, high-yielding varieties of wheat will be fundamental to meeting these goals,” said University of Liverpool professor and team member Anthony Hall.

At the end of 2009, scientists at Kew Gardens and the Natural History Museum in London proposed that many plants can behave like animals. They said that carnivory in plants may be far more widespread than previously thought and suggested that many cultivated plants are at least partly carnivorous. For example, many petunias (Petunia) and some potato species have sticky hairs that trap insects. Other sticky-leaved species such as some geraniums (Geranium) have been shown to produce digestive enzymes that can absorb the remains of insects. The team suggested that there is a sliding scale of carnivory, ranging from mildly carnivorous forms, such as petunias, to full carnivores with active traps, such as the Venus’ flytrap (Dionaea muscipula).

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